This invention relates to a composition board and particularly to a particle board of the general type widely used in the construction and furniture industries and in other industrial and domestic applications.
Several forms of particle board are known. Those of the highest quality in terms of strength, stability, durability, and certain other features traditionally comprise a mixture of wood chips (usually a softwood), a filler material, and a binder. There may also be other constituents. The wood chips, which are generally in form of flakes that are largely superimposed on each other in the plane of the board, supply structural strength and certain characteristics such as the ability to receive screws. These characteristics arise from the fibrous nature of the chip material, with the fibres having a linear characteristic and the fibres in each particle being substantially parallel to one another.
The filler material has virtually no structural strength but provides bulk and lends consistency to the board. The traditional filler material is sawdust, which is cheap and readily available and has generally suitable physical and chemical properties.
The binder or glue may be of many types, the common modern types being chiefly phenolic resins and the more economical urea formaldehyde. Other substances, particularly thermosetting resins or even thermoplastic resins, with the possible addition of other constituents to provide special features, are also commonly used. The cost of the modern resins in high-quality particle boards may be as much as 75% or more of the total cost of the materials.
Numerous attempts have been made to reduce the cost of the traditional particle board, particularly in recent years when the cost of lumber (which is used in the form of round logs in the manufacture of high-quality particle board to provide the structural chips) and resin has been steadily rising. These attempts have centred largely around the introduction of cheaper materials.
As a substitute for wood chips, begasse has been resorted to on a large scale, and various grades of bagasse board are now established products in many countries. Bagasse is available cheaply as a waste product from sugar mills and is hence far cheaper than logs. It has however certain disadvantages, one of them the fact that it is less dense than wood and requires expensive machinery to compress it satisfactorily. Further it is accompanied by a substantial quantity of pith which is structurally weak and must be removed. It also requires more resin than do wood chips to bind it in the finished board, so that the binder component becomes more costly and the board, being more resinous, is also less easily worked by conventional woodworking tools. Generally, boards containing a relatively high bagasse content are in the lower quality range of particle boards.
Numerous vegetable waste materials have been used as filler materials or as other constituents of particle boards. Among those materials described in the prior art are coffee beans and coffee grounds. Coffee is an endocarp which, at least after it has been roasted, is hard and tough. In the manufacture of instant coffee, the beans are roasted, ground and processed to remove the soluble solid content. The resultant particles still contain a relatively high oil content and do not readily absorb binder resins, so that the usefulness of coffee as a filler substance is generally limited in products such as particle board. Particle boards with a high coffee content would in fact normally be among the lower quality grades. Coffee grounds are however available in substantial quantities as a waste product which is usually dumped or incinerated to dispose of it. Attempts have been made to use certain thermoplastic properties which coffee possess at high temperature and pressure in order to mould it as a structural material in its own right (as described for instance in U.S. Pat. No. 3,686,384 of Leslie A. Runton), but these temperatures and pressures are higher than those conveniently available in conventional equipment for manufacturing particle board.
Considerable efforts have also been made to use other endocarps and the shells, husks, barks, and stalks of many plants as constituents of pressed or moulded products, often in the form of a flour which has certain thermoplastic or thermosetting properties as well as being a filler, carrier or extender or the like. Examples of such materials (including coffee in some cases) are described in, for instance, U.S. Pat. Nos. 2,319,182 and 2,440,789 of Edward van der Pyl, and other lignocellulosic materials in U.S. Pat. No. 3,968,294 of Paul Robitschek et al.
An example of a particle board utilising materials which are commonly regarded as wastes is described in U.S. Pat. No. 3,927,235 of Poo Chow. In this patent the board is described as a laminate structure in which a central core contains, as a major ingredient, plant material obtained from a part other than the stalk. Coffee beans are among the materials mentioned as such a constituent. The two surface layers are on the other hand composed mainly of a stalk material such as bagasse. Urea formaldehyde is mentioned as a suitable binder material. This board, while being potentially inexpensive compared with the traditional wood particle board, would not be of high quality if it contained coffee since its central core, with more than 50% coffee, would be structurally weak, the coffee particles lacking the bonding and fibrous properties that are present in the wood chips used in traditional high-quality boards.